1. Field of the Invention
This invention relates generally to acyclic terpenoid compounds such as citronellol, geraniol and their derivatives which possess tyrosinase inhibitory, melanin-formation inhibitory, and skin whitening activities.
2. Description of Related Art
Skin pigmentation and tanning are related to the amount of melanin in epidermal melanosomes. In the melanosomes, tyrosine is oxidized to dopa and dopaquinone by the enzyme tyrosinase; the resulting intermediate compounds polymerize to form the brown-black melanin pigment. The formation of melanin is believed to be a defensive mechanism in humans which protects their skin from harmful ultraviolet rays. However, the excessive formation of melanin following prolonged sun exposure or due to disorders of epidermal melanin units is responsible for melasma, ephelides, and pigmented cosmetic dermatitis.
Although the precise mechanism of excessive melanin formation has not been fully elucidated, the activation of tyrosinase appears to be a significant factor. Thus, the development of chemical agents capable of modulating the enzyme activity of tyrosinase would have considerable value for the control of the above-noted undesirable skin conditions.
Some tyrosinase inhibitors are known already. These inhibitors include lipoic acids, thiopronions, glutathiuones, pantetheines, flavonols, hydroquinones, pyrones, and kojic acids. Among them, arbutin, one of the hydroquinones, has been used widely. Illustrative references directed to such tyrosinase inhibitors follow.
Japan Kokai 1-305,025, 1-305,026, 2-193,917, and 2-193,918 disclose alkanoic acids, the esters thereof, and unsaturated fatty acids for inhibition of biosynthesis of tyrosinase. Japan Kokai 3-109,319 discloses 5-farnesyl-6-methylresorcinol (neogrifolin) that is a tyrosinase inhibitor.
There has been a need for tyrosinase inhibitors capable of effectively inhibiting the activity of tyrosine and which could be used on a long term basis without undesirable side effects on the human skin. In spite of research activities, up to now, no one has recognized that certain acyclic terpenoid compounds or the derivatives thereof could inhibit tyrosinase or melanin formation. Accordingly, this invention provides methods for inhibiting tyrosinase or melanin formation in living cells. Such methods desirably include topical treatment of humans with a composition containing the acyclic terpenoid compounds.